Which of the following objects is found almost exclusively in the halo of the Milky Way?

Globular clusters are dense collections of stars that are primarily found in the halo of the Milky Way. These clusters are ancient, typically containing stars that are much older than those found in the galactic disk. Their formation occurred early in the history of the galaxy, and they are typically found orbiting the Milky Way in a spherically distributed halo.

The halo itself is a region surrounding the main disk of the galaxy, which contains very old stars, globular clusters, and dark matter, but is relatively devoid of the gas and dust needed for star formation. Globular clusters can contain hundreds of thousands of stars tightly packed together, and their presence in the halo helps astronomers study the early stages of the Milky Way as well as the dynamics of the galaxy as a whole.

In contrast, open clusters and blue stars are predominantly found in the disk of the galaxy, where star formation is ongoing. Red giants are a later stage of stellar evolution that can be found throughout the galaxy, including the disk, but they do not characterize the halo like globular clusters do. Hence, globular clusters are the most distinctive objects associated with the Milky Way's halo.